Type bar drive



May 31, 1960 R. A. DONNAN ETAL 2,938,615

TYPE BAR DRIVE 2 Sheets-Sheet 1 Filed Dec. 20, 1955 INVENTORS ROBERT A.DONNAN THURS ON H.TOEPPEN (I (fil ATTORNEY May 31, 1960 R. AI DONNAN E2,938,615

TYPE BAR DRIVE 2 Sheets-Sheet 2 Filed Dec. 20, 1955 FVIIIIII INVENTORSROBERT A. DONNA THURST N H.To (u M ATTORNEY TYPE BAR DRIVE Robert A.Donnan, New Paltz, and Thurston H. Toeppen, Hyde Park, N.Y., assignorsto International Business Machines Corporation, New York, N.Y., acorporation of New York Filed Dec. 20, 1955, Ser. No. 554,185

4 Claims. (Cl. 197-17) This invention relates to typewriters and moreparticularly to an improved tripping mechanism and cam control for apower driven type bar drive.

In conventional power driven type bar mechanisms, examples of which areshown in U.S. Patents 2,723,740 and 2,796,966, a cam is held normallyout of engagement from a continuously driven power source, such as apower roller, and then pushed into engagement with the power roll toinitiate a type bar print stroke.

In order to keep the conventional cam tripping force at a minimum, theclearance between cam and power roller must be as small as possible.Because of these close tolerances, and under certain type bar bounceconditions, unwanted repeat print strokes take place.

It follows that it is a first object of this invention to provide a newtripping mechanism for-a power driven type bar drive.

It is a further object of this invention to provide an improvedinterengagement between a type bar and its driving cam wherein any typebar rebound will not cause an unwanted repeat stroke.

It is a still further object of this invention to reduce the fingershock or jar which a typist senses during a conventional type bar printstroke.

It is a further object of this invention to provide an improved camcontrol for a power driven type bar.

It is a still further object of this invention to provide an improvedcombined cam control and tripping mechanism for a power driven type bardrive.

Other objects of the invention will be pointed out in the followingdescription and claims and illustrated in the accompanying drawings,which disclose, by way of example, the principle of the invention andthe best mode, which has been contemplated, of applying that principle.

Briefly, this invention relates to an improved power driven type bardrive cam control and tripping mechanism therefor, wherein the cam ismounted on an intermediate lever that is spring urged into engagementwith the power roll and accordingly when a key lever is depressed thecam is tripped for biased movement into engagement with, rather thanpushed into engagement with, the power roll, and since the cam is springurged into engagement with the power roll, the key lever is completelydisengaged from the intermediate lever at time of cam knock off, hencethe typist does not sense any finger shock during a type bar printstroke.

Referring to the drawings, Fig. l is a side elevation showing thedetails of a type bar drive mechanism.

Fig. 2 is an enlarged view of the tripping mechanism for the type bardrive.

Fig. 3 is an enlarged view of the cam control mechanism.

The type bar structure comprises a cam lever 2 which is pivotallysupported at 4 on a transverse rod which extends across the typewriter.It is to be understood that normally a plurality of cam levers aresupported on the rod 4, one for each type bar of the machine.

nited States Patent Patented May 31, 1960 Each type bar 6 is pivotalabout a support fulcrum 10 r and connected via a link 8 to the cam lever2. When the cam lever 2 is rocked clockwise about its pivot 4, the typebar 6 will be driven counterclockwise about itssupport 19 into printingengagement with a platen 12.

The driving means for cam lever 2 is a cam 14 which is selectivelyengageable with a continuously driven power roll 16. The cam 14, whichis pivotally supported on a pin 15 carried by an intermediate lever 18,is normally spaced from the power roll a slight distance. Theintermediate lever is pivotally supported on a pin or stud 20 carried bythe cam lever 2. The intermediate lever 18 has an ofiset finger 22 whichis slidable relative to cam lever 2 within the limits of a slot 24formed in the cam lever.

The intermediate lever has a pair of bent over ears 26, 28, and the camlever has bent over ear 30. A spring 32 is hooked into the car 30 of thecam lever to engage stud 26 as well as the ears 26 and 28 of theintermediate lever 13. With this arrangement of parts, there is a biason the ear 28 tending to rotate the intermediate lever clockwise aboutstud 2t), and a bias on the car 26 tending to rotate the intermediatelever counterclockwise about the stud 20. Since the distance between ear26 and stud 26' is greater than the distance between ear 28 and stud2%), then, with the parts arranged as in Fig. 1, there is an unbalancedtorque which tends to rotate the intermediate lever counterclockwiseabout stud 2G.

This unbalanced torque is utilized to rock cam 14 into engagement withthe power roll 16, consequently the intermediate lever is equipped withan integral trip latch 34 which engages a trip finger 36 extending froma key lever 38. The latter is pivotally supported about a fulcrum rod 49which extends transversely of the typewriter so as to support one keylever for each type bar driving mechanism.

With this structure, it is apparent that when the trip finger 36 hasbeen depressed out of blocking engagement with the latch 34, spring 32acts to rock the intermediate lever 18 counterclockwise (moving triplatch 34 to the Fig. 2 position) to bring cam 14 into engagement withthe power roll, thereby initiating a type bar print stroke.

The power roll 16 drives cam 14 towards its high dwell clockwise aboutits pivot 15 thereby rocking cam lever 2 clockwise about its pivot 4.That is, an extension of pivot 15 drives cam lever 2 until a flange 50on the intermediate lever 18 engages an impression control cam 52, thena shift takes place wherein the driving relation between theintermediate lever 18 and the cam lever 2 is via the pivot pin 20 ratherthan via pin 15. This change in drive is explained completely in US.Patent 2,796,966.

After the cam 14 has rotated to its high point, then, as a result of themomentum of the parts, the cam lever will continue to rock in freeflight until the type bar 6 strikes the platen. During this free flightof the cam lever, cam 14 is restored to its normal position shown inFig. 1 through the interaction of a spring 54 in engagement with a fiatsurface on the under side of the cam 14. The type bar 6 and its camlever 2 are restored to rest position (Fig. 1) by a spring 48.

One of the important elements of this improved type bar cam control isthat the cam 14 cannot jam to stall the power roll as could happen withconventional type bar driving mechanisms when type bars clash, and locknear printing position. With this improved cam control, the cam wouldmerely roll over under such conditions and make a complete revolutionabout its pivot 15 whereupon the spring 54 would again restore the camto its normal position shown in Fig. 1.

show the position of these parts when the cam lever 2 has been'rock'edto a type bar print position.

his then apparent that a blocking device is required to prevent repeatstrokes, otherwise if key lever 38 were held depressed'the trip latch 34would cyclically move to its Fig. 2=position and a repeat stroke wouldoccur.

A blocking device or latch guard 42 is'pivotally and slidably supportedon a stud 44 carried by the key lever 38. The latch guard 42 is biasedby a spring 47 against the trip finger 36 in such a position that ashoulder 46 on the guard is normally spaced a short distance beyond theright edge of the finger 36, as shown in Figs. 1 and 3; The trip latch34 normally engages the end of the finger'36 and lies below the shoulder46. When the key lever 38 is depressed, the latch guard 42 is heldagainst movement with the lever since the shoulder 46 rests upon the'latch 34. The end of the finger 36 is moved out of alignment with theend of the trip latch upon depressing. the key lever, and theintermediate lever 18 is rocked counterclockwise so that the trip latchassumes a position relative to the finger 36 as shown in Fig. 2. The cam14 is engaged with the power roll and causes the intermediate lever torock clockwise. As the trip latch 34 moves beyondthe shoulder 46, thelatch guard 42 snaps'down to'the'position shown in Fig; 3. With latchguard 42 in its Fig. 3 position-e.g. when the key lever is helddepressed, the trip latch 34 will strike latch guard 42 (see dottedposition Fig. 3) and thus hold cam 14 away from the power roll 16. Whenkey lever 33 is restored to its Fig- 1 position, the trip latch 34'willslide off latch guard 42 and assume its Fig. 1 rest position.

Specific reference is made again to the mechanism for moving cam 14 intoengagement with power roll 16. That is, in the prior art, (U.S. Patents2,723,740 and 2,796,966) the power cam is pushed into engagement withthe power roll under the direct action of the key lever. In the subjectmechanism, however, the cam en'- gages the power roll under the force ofthe spring 32 and the sole function of the key lever is to release theintermediate lever to permit spring 32 to act. With this structure, theonly force that restrains the key lever 38 is the spring 58 and the endfrictional force between the trip finger 36 and the trip latch 34. Ifthese interacting surfaces are made smooth enough it will take only avery' slight amount of force to depress the key lever to bring the caminto engagement with the power roll, since the spring 58, which holdsthe outer end of the key lever in a guide comb .60, can be of a forcesimply great enough to overcome the gravitational effect of the keylever 38 whereupon a very minimum force will be required to depress thekey lever to initiate a type bar print stroke.

While there'have been shown and described and pointed out thefundamental novel features of the invention as applied to a preferredembodiment, it will be understood that various omissions andsubstitutions and changes in the form and'details of the deviceillustrated and in its operation may be made by those skilled in the artwithout departing from the spirit of the invention.

It is the intention therefore, to be limited only as indicated by thescope of the following claims.

What is claimed is:

l. A type bar drive mechanism for a typewriter comprising, incombination, a cam lever, means operatively connecting said cam lever tosaid type bar, an interme-- diate lever pivotally mountedon said camlever, a cam rotatably supported by said intermediate lever, a powerroll, spring means urging said intermediate lever in a direction toengage said cam with said power roll, a manually operable key lever,means on said key lever normally engaging said intermediate lever forholding the latter against the urging ofsaid spring means, said lastmentioned means moving out of engagementwith prising, in combination, acam'lever, means operatively connecting 'said cam lever to said typebar, an intermediate lever'pivotally mounted on said cam lever, acam'ro- 'tatably supported by said intermediate lever, a power roll,spring means urging'said intermediate lever in a'direction to engage'saidcam with said power roll, a manually operable' key'lever, afinger formed integral with said' keylever, a' latch" arm on saidintermediate lever and having a projecting portion normally engaging theend of said finger for holding said intermediate lever against theurging ofsaid spring means, said finger moving out of engagement withsaid projecting portion on op erationof said key leverto: permitengagement of said cam with" said power'roll and'etfect a drivingof'said type bar from a rest position to a print position, and a guardmember mounted on said key lever and cooperating with said finger toprovide a stop for said projecting. portion when said key lever'is helddepressed, said stop operating to hold said intermediate lever in aposition with said cam free of said power roll.

3; The mechanism of claim 2 in which said guard member is pivotallymounted on said key lever for en'- gagement with said finger, and aspring normally holding-said guard member against said finger in aposition slightly overlying its'end, said gu'ardmember being held bysaid projecting portion against'movement with said finger on depressionof said key lever, said intermediate lever operating on the driving ofsaid cam by said power -roll to move said projecting portion away fromsaid gitudinal movement of the latter whereby engagement of saidprojecting portion -with said guard member forces the latter against theaction of said spring into alignment with the end of said finger.

References Cited in the file of "this patent UNITED STATES PATENTS1,153,582 Steiner Sept. 14, 1915 1,173,321 Steiner Feb. 29, 19161,737,439 Stickney Nov. 26, 1929" 2,531,891 Reppert Nov..28, 1950

